Alpha-1 antitrypsin

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Also known as: A1AT; AAT; α1-antitrypsin

At a Glance

Why Get Tested?

To help diagnose the cause of early onset emphysema and/or liver disease. To establish the risk of developing alpha-1 antitrypsin-related emphysema and/or liver disease and the likelihood that children might inherit the risk

When to Get Tested?

When you show signs of liver disease as an infant or young child, when you develop emphysema (a disease that damages the lungs) before age 40, or when you have a close relative with alpha-1 antitrypsin deficiency

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


The Test Sample

What is being tested?

Alpha-1 antitrypsin (A1AT) is a protein that is produced in the liver and released into the bloodstream. A1AT works by inactivating several enzymes but primarily the enzyme elastase in the lungs. Elastase is an enzyme produced by neutrophils (a type of white blood cell) and it is part of the body’s normal response to injury and inflammation. Elastase breaks down proteins so that they can be removed and recycled by the body but, if its action is not regulated by A1AT, elastase will also begin to break down and damage lung tissue.

A1AT is the product of the SERPINA1 gene, commonly known as the protease inhibitor (Pi) gene, of which everyone has two copies. Each Pi gene copy is responsible for producing half of the body's A1AT. If there is a change (called a 'mutation') in one or both of the gene copies, then less A1AT and/or A1AT that does not work properly, is produced. If the resulting A1AT production drops down to 30% of normal or less, then the affected patient will experience a disorder called alpha-1-antitrypsin deficiency. Patients with this disorder are at a considerable risk of developing emphysema (a progressive lung disease) in early adulthood. If they smoke, or are exposed to occupational dust or fumes, the lung damage tends to occur sooner and be more severe.

If the A1AT produced does not work properly it tends to accumulate in the liver cells that produce it. As it builds up in these cells, the A1AT forms abnormal protein chains and begins to destroy the cells and damage the liver. About 10% of those affected with A1AT deficiency will have liver disease as a newborn. Many improve on their own but in severe cases these infants may require a liver transplant to survive. A1AT deficiency is currently one of the most common reasons for a liver transplant in the paediatric population.

The amount and function of the A1AT created depends on the mutation inherited. While there are more than 70 different variations (alleles) in the Pi gene, only a few are common. Most people in Australia, about 90%, have two copies of the normal M gene (MM). The most common of the abnormal forms are S and Z. Those people with:

  • One copy of M and one of S or Z (MS or MZ) will produce reduced amounts of A1AT but should have enough to protect themselves. They will be carriers of the condition, however, and can pass it on to their children
  • Two copies of S (SS) may have no symptoms or be moderately affected (they produce about 60% of the required A1AT)
  • One copy of S and one of Z (SZ) are at an increased risk of developing emphysema (they produce only about 40% of normal A1AT)
  • Two copies of Z (ZZ) are the most severely affected (they only produce about 10% of the required A1AT) along with those who have one or two copies of rare forms of the Pi gene which are 'null' (they do not produce any A1AT)

Types of A1AT tests
Different A1AT tests can be used to measure the amount of A1AT, determine which types and concentrations of A1AT protein are present, and determine which Pi gene alleles a patient has.

  • Alpha-1 antitrypsin, this test measures the total amount of A1AT present
  • Alpha-1 antitrypsin phenotype, separates out the different variants of A1AT protein being produced and compares them to known patterns. It also allows an estimation of the amount of each type present. A protein electrophoresis test is sometimes used to screen for a severe A1AT deficiency
  • Alpha-1 antitrypsin DNA testing, genetic testing that can be done to identify which protease inhibitor gene mutations (Pi gene alleles) are present. Only the most common mutations are usually tested (M, S, Z). This test can be used to help evaluate affected patients and their family members
Doctors also occasionally test for the level of A1AT in the faeces (bowel motion). This is done when the doctor suspects the person is losing protein from the gastrointestinal tract and is NOT part of testing for alpha-1 antitrypsin deficiency.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.